upload --dry-run and tests fixes

[memsharded]

Changelog: Feature: Add conan upload --dry-run equivalent to 1.X conan upload --skip-upload.
Docs: conan-io/docs#3274

Also, recover or remove some xfailed tests (the PR started there, then realized that the --dry-run feature was not there, and I recall it being used by some users in 1.X

[AbrilRBS]

Is there any other command where this functionallity might be missing?

[memsharded]

Is there any other command where this functionallity might be missing?

This was the only one in Conan 1.X (btw, I am open to keep the --skip-upload 1.X syntax).
One use case was doing all the heavy compressions and integrity checks in one pass, then uploading all, so the actual upload was faster (compression can take a lot of time for large packages), improving a bit the atomicity of the upload. Also, the idea is that this will also support the upload via Artifactory API, but we can discuss this, if premature I can remove it, it was not the intent of this PR, but to fix tests.

I am not sure other commands do need it. For download/remove we already have the package-lists feature, that lists you the things that will be removed/downloaded.

[AbrilRBS]

Thanks for the extra context, quite helpful :)

btw, I am open to keep the --skip-upload 1.X syntax

I like the --dry-run syntax better